Award Ceremony Speech

About thirty years ago, for the first time, we humans were able
to view our planet from space. We saw white cloud formations,
blue oceans, green vegetation and brown soils and mountains. From
space, we could view and study the earth as a whole. We have come
to understand that we influence and are influenced by our
biosphere, our life zone. One of the tasks of science is to
describe and explain how this happens. In their research on the
chemical reactions occurring in the earth's atmosphere, the 1995
Nobel Laureates in Chemistry - Paul Crutzen, Mario Molina and
Sherwood Rowland - have adopted this global perspective.

The sun is the engine of life. Solar
radiation is the source of energy for nearly all living
organisms. But only some of the sun's rays are beneficial. It
also emits ultraviolet radiation that harms living beings. Many
of us have painful experience of excessive sunbathing. Life in
the forms we are familiar with is the result of photosynthesis in
green plants, which transforms the carbon dioxide in the air into
biomass and oxygen. It has taken hundreds of millions of years
for the biosphere to develop the atmospheric composition we have
today. In the upper atmosphere, or stratosphere, solar radiation
can transform oxygen into ozone. The highest ozone concentrations
are found at an altitude of between 15 and 50 km. This ozone
layer absorbs the sun's ultraviolet radiation very effectively,
thereby reducing hazardous radiation on the earth's surface.
This, in turn, makes efficient photosynthesis possible. Here we
see an example of a feedback mechanism between the chemistry of
the biosphere and the atmosphere. If it is disrupted, there may
be serious consequences for life on our planet.

This year's laureates have made a series of
major contributions to our knowledge of atmospheric chemistry.
This has included studying how ozone is formed and decomposes and
how these processes can be affected by chemical substances in the
atmosphere, many of them the result of human activity. In 1970
Paul Crutzen demonstrated that nitrogen oxides, formed during
combustion processes, could affect the rate of ozone depletion in
the stratosphere. He suggested that dinitrogen monoxide,
popularly known as "laughing gas" and formed through
microbiological processes in the ground, could have the same
effect. He has also studied the formation of ozone in the lower
atmosphere. Ozone is one ingredient of "smog," which is formed by
the influence of solar radiation on air pollutants, especially
exhaust gases from motor vehicles and other combustion systems.
Whereas stratospheric ozone is a prerequisite for life,
tropospheric ozone is strongly toxic and harmful to most
organisms, even in small quantities.

In 1974 Mario Molina and Sherwood Rowland
showed that chlorine compounds formed by the photochemical
decomposition of chlorofluorocarbons (CFC or "Freon" gases) could
decompose the stratospheric ozone. They presented detailed
hypotheses on how these complicated processes occurred.

The discoveries of the three researchers
have an unusually close connection with the consequences of
modern technology. Supersonic aircraft release nitrogen oxides in
the stratosphere. Motor vehicles and stationary combustion plants
release the same substances into the lower atmosphere. CFC gases
from refrigerators and air conditioners, and in the form of
aerosol spray propellants - combined with a "throwaway culture" -
result in large-scale emissions of chlorine compounds into the
atmosphere. The findings presented by this year's laureates in
chemistry have had an enormous political and industrial impact.
This was because they clearly identified unacceptable
environmental hazards in a large, economically important sector.
Their models were also subjected to very rigorous examination
which eventually confirmed the main features of their original
hypotheses. One obvious result is an international agreement
known as the Montreal Protocol, which regulates the manufacture
and use of CFCs.

Perhaps the most spectacular observation of
changes in the stratospheric ozone content was made in 1985 over
Antarctica by Joseph Farman and his colleagues. They observed a
rapid and dramatic depletion of ozone in the polar region when
sunlight returned after the polar night. The ozone content then
built up to more normal levels during the subsequent polar summer
and winter, after which the process was repeated. This recurring
"ozone hole" was completely unexpected. Eventually a scientific
explanation was found, mainly through the research of Susan
Solomon, with important contributions from this year's laureates
in chemistry as well.

Professor Crutzen, Professor Molina, and
Professor Rowland,

You have demonstrated the importance of homogeneous and
heterogeneous chemical processes in the earth's atmosphere. You
have developed models that combine these data with knowledge of
the large-scale transport processes in the atmosphere, and how
these models can be utilized as a forecasting tool to evaluate
the consequences of emissions of anthropogenic substances of
various kinds. You have thereby not only created a clearer
understanding of fundamental chemical phenomena, but also of the
large-scale and often negative consequences of human behavior. In
the words of Alfred Nobel's will, your work has been of very
great "benefit to mankind." It is a privilege to congratulate you
on behalf of the Royal Swedish Academy of Sciences, and I now ask
you to receive your Nobel Prizes from the hands of His Majesty
the King.